The present invention relates to monitoring the progression or stage of disease in breast cancer patients. More particularly, the invention relates to such monitoring methods based on measurement of cancer marker blood levels.
A number of substances have been determined to be useful markers in monitoring the course of various cancer types. Some useful markers that have been identified are oncofetal antigens such as carcinoembryonic antigen (CEA) and alpha-fetoprotein, tissue-specific antigens such as prostate-specific antigen (PSA), and mucin antigens such as those conventionally known as CA-125 and CA-19-9. Immunoassays for antigens such as these are typically used as confirmatory tests at the time of diagnosis and subsequently for monitoring patient status. Occasionally, the use of such tests crosses the boundaries of tumor type (for example, the use of CEA tests in colon, breast, and lung cancer, and alpha-fetoprotein in hepatocellular and testicular cancer), but the utility of each test type is foremost for a single tumor type (for example, PSA for prostate cancer and CA-125 for ovarian cancer).
A family of antigenic proteins have been identified which are genetically and immunologically related to CEA (Thompson, J. and W. Zimmerman (1988) Tumor Biol. 9, 63-83; and Barnett, T. and W. Zimmerman (1990) Tumor Biol. 11, 59-63). Among these are the nonspecific cross-reacting antigens (NCAs), the trans-membrane antigens designated biliary glycoprotein (BGP, and sometimes referred to as TM-CEAs), and the family of pregnancy-specific .beta.-glycoproteins (PSGs) (for a description of the accepted nomenclature of these genes and their protein products, reference can be made to: Barnett, T. and W. Zimmerman (1990) Tumor Biol. 11, 59-63). Molecular cloning of the CEA gene family has enabled the identification of 22 members, of which 20 are probably expressed (Frangsmyr, L. et al. (1992) Tumor Biol. 13, 98-99; and Hammerstrom, S. et al Tumor Biol. 13, 57). The results of molecular genetic analysis have given a better understanding of the complex group of glycoproteins in the CEA gene family.
NCA was originally described as a component of normal tissue which cross-reacted with antibodies raised to CEA (Mach, J.-P. and G. Pusztaszeri (1972) Immunochemistry 9, 1031-1034; and von Kleist, S., Chavenel, G. and P. Burtin (1972) Proc. Natl. Acad. Sci. USA 69, 2492-2494). As such, NCA was considered a potential nontumor derived interferant in assays for CEA. Molecular cloning identified one species of NCA of calculated M.sub.r 37,000 designated by one group as NCA-BT (Barnett, T., Goebel, S. J., Nothdurft, M. A. and J. J. Elting (1988) Genomics 3, 59-66) to denote the breast tissue origin of the cloned cDNA, and by others as NCA (Tawaraji, Y. et al. (1988) Biochem. Biophys. Res. Commun. 150, 89-96; and Neumaier, M. et al (1988) J. Biol. Chem. 263, 3203-3207). This single NCA species has since been termed NCA 50/90 (Kolbinger, F., Schwarz, K., Brombacher, F., von Kleist, S., and Grunert, F. (1989) Biochem. Biophys. Res. Commun. 161, 1126-1134) because it was now known to be processed into two mature isoforms of M.sub.r 50,000 and M.sub.r 90,000 which have different degrees of glycosylation. A second and distinct NCA gene was subsequently identified by molecular cloning from leukemic cells that codes for an M.sub.r 95,000 glycoprotein (Kuroki, M. et al (1991) J. Biol. Chem. 266, 11810-11817). This latter NCA has been termed NCA 95.
Early studies also identified a cross-reacting antigen from adult stools and from meconium which, for historical reasons, was termed NCA-2 (Burtin, P., Chavenel, G. and H. Hirsch-Marie (1973) J. Immunol. 111, 1926-1928). The designation of this antigen as NCA is, however, a misnomer. It has been identified as a proteolytic fragment of CEA since the first 30 amino acids of the meconium-derived NCA-2 are identical in sequence with CEA (Siepen, D. et al (1987) Biochem. Biophys. Res. Commun. 174, 212-218). In contrast, cDNAs for NCA 50/90 and NCA 95 have been described and code for distinct and different amino acid sequences in this region. Indeed, a recent report suggests that variability in CEA results obtained with different commercial kits may be due to interference with NCA-2 (O. P. Bormer (1991) Clin. Chem. 37, 1736-1739).
Given the improved understanding of the CEA gene family resulting from molecular cloning analysis, monoclonal antibodies can now be identified which recognize specific family members and do not cross react with closely related molecules. Previous attempts to raise antibodies to NCA have been plagued with the problem of cross reactivity with CEA family members. This may explain why NCA has been considered a poor serum marker for cancer diagnosis and monitoring (Shively, J. E., Spayth, V., Chang, F.-F., Metter, G. E., Klein, L., Present, C. A., and C. W. Todd (1982) Cancer Res. 42, 2502-2513; and Burtin, P., Chavenel, G., Hendrick, J. C. and N. Frenoy (1986) J. Immunol. 137, 839-845). It has been further speculated that NCA-specific monoclonal antibodies such as are now widely accepted for CEA and other antigens would be very difficult to develop (Burtin, P. et al., supra).
In addition, it is now clear that members of the CEA gene family are differentially expressed by various tumor types. For example, it is well known that CEA is expressed in most if not all colorectal carcinomas, while expression is limited to a minority of breast carcinomas. Prior to the generation of specific monoclonal antibodies, attempts to quantitate NCA levels in the serum of cancer patients were confounded by the presence of other CEA gene family members that cross reacted with the antibodies being used. However, because of the successful production of monoclonal antibodies specific to NCA 50/90, it is now possible to determine the incidence of elevated NCA 50/90 protein in different cancer types.
Although there have been reports of monoclonal antibodies specific for NCA 50/90 (Chavenel, G., Frenoy, N., Escribano, M. J. and P. Burtin (1983) Oncodev. Biol. and Med. 4, 209-217; and Yeung, M., M.-W. Hammerstrom, M. L., Baranov, V. and S. Hammerstrom (1992) Tumor Biol. 9, 119), there have been no reports of a monoclonal antibody which binds to NCA 50/90 but does not recognize any other CEA family members including CEA, NCA 95, NCA 2, BGP or PSG. Similarly, several reports have suggested that NCA may be elevated in the serum of cancer patients (von Kleist, S., Troupel, S., King, M. and P. Burtin (1977) Br. J. Cancer 35, 875-880; and Wahren, B., Gahrton, G., Ruden, U. and S. Hammerstrom (1982) Int. J. Cancer 29, 133-1.37; and Harlozinska, A., Rachel, F., Gawlikowski, W., Richter, R. and J. Kolodziej (1991) Eur. J. Surg. Oncol. 17, 59-64; and Reck:, W., Daniel, S., Nagel, G., Hirn, M., von Kleist, S., and F. Grunert (1992) Tumor Biol. 13, 110-111), but these measurements utilized antibodies that have not been shown to recognize NCA 50/90 to the exclusion of other CEA-related molecules. In addition, there have been no reports of a correlation between blood NCA levels and the clinical status of any particular cancer patients.
Previous attempts to quantitate the level of NCA 50/90 in the serum have been hampered by the lack of a suitable standard. Measurements of NCA in blood have shown mean values in serum from normal individuals of from 30 ng/ml (Harlozinska, A., et al. supra) to 130 ng/ml (von Kleist, S., Troupel, S., King, M. and P. Burtin (1977) Br. J. Cancer 35, 875-880). This is due to the use of biochemically purified NCA as a standard to calibrate immunoassay measurements of NCA in blood and blood fluids. Just as the monoclonal antibodies have not been demonstrated to specifically recognize NCA 50/90, neither has the purity of the NCA standard preparations been determined.